clk: mediatek: clk-mt7629: Add check for mtk_alloc_clk_data

Add the check for the return value of mtk_alloc_clk_data() in order to
avoid NULL pointer dereference.

Fixes: 3b5e7486 ("clk: mediatek: add clock support for MT7629 SoC")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Link: https://lore.kernel.org/r/20230912093407.21505-5-jiasheng@iscas.ac.cn


Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>